• The “steady state” that cell exists in normally.
• An equilibrium of the cells with their environment for adequate function.
• When disturbed there is a predisposal for the onset of pathology.
Cells Adapt to Changes (Stimuli, Stressors)
Adaptations occur on a spectrum. Some are:
Helpful: hypertrophy or hyperplasia increase organ size so it can function better
More harm than good. Example: increased organ size requires more blood supply. If that is not available, organ becomes ischemic
Adaptation can involve:
• change in cell size or number
• change to different type of cell
On Application of Stress
• Atrophy (brown atrophy)
• Metaplasia: simple columnar to stratified squamous (lungs)
• Dysplasia: some loss of control as in cervix
TYPES OF ADAPTATION
SHRINKAGE OF CELLS
Due to decreased work load (e.g., decreased size of uterus following child birth, or disease)
Example of Atrophy
In the size of cells which results in enlargement of the organs , without any change in the no. of cells
It is mostly seen in cells that cannot divide, such as skeletal muscle (pumping iron), and cardiac muscle (hypertension).
These changes usually revert to normal if the cause is removed.
Hypertrophy is mediated by different mechanisms.
• Dividing cell →Hypertrophy + Hyperplasia
• Non-dividing cell → Hypertrophy
Causes of Hypertrophy
• Enlarged size of uterus in pregnancy
• Action of estrogenic hormones
• Hypertrophy of cardiac muscle
• Hypertrophy of Smooth muscle
• Hypertrophy of skeletal muscle
• Compensatory Hypertrophy
Increased number of cells in an organ or tissue.
Hyperplasia may sometimes co-exist with hypertrophy.
Hyperplasia can be classified as:
hormonal (e.g., breast and uterus during pregnancy)
Degeneration of liver following partial hepatectomy. Various growth factors and interluekins are important in such hyperplasia.
excessive hormonal stimulation viral infection (papilloma viruses); neoplasms
Example of Hyperplasia
Transformation or replacement of one adult cell type to another adult cell type (e.g., the change from columnar to squamous cells in respiratory tract, from squamous to columnar in Barrett esophagitis).
Metaplasia also occurs in mesenchymal tissue (e.g., formation of bone in skeletal muscle).
Metaplastic changes usually result from chronic irritation.
Metaplastic changes seem to precede the development of cancer, in some instances.
Types of Metaplasia
• Epithelial Metaplasia
o Squamous metaplasia
o Columnar metaplasia
• Mesenchymal Metaplasia
• Osseous metaplasia
• Cartilagenous metaplasia
EXAMPLES OF METAPLASIA
The term “dysplasia” means “disordered cellular development”
It often accompanied by metaplasia & hyperplasia, thereby also referred as Atypical Hyperplaisa
• Short Duration → Reversible
• Long Duration → Carcinoma Cancer
It may occur due to Chronic Irritation or Prolonged inflammation.
Example of Dysplasia
• Adaptable within physiological limits.
• Heat Shock Proteins (HSPs): Can respond to injury by producing cell stree proteins.
• Demand met by Hypertrophy & Hyperplasia.
• Demand met by Atrophy.
• Apoptosis : Cell loss can be achieved from Programmed cell death
• Tissue can adapt to demand by a change in differentiation known as Metaplasia.